An alternator pulley unit with a built-in one-way clutch of the present invention is utilized for driving an alternator serving as a generator for vehicles, by fixing the pulley unit to an end of a rotation shaft of the alternator, and spanning an endless belt between the pulley unit and a drive pulley fixed to an end of a crank shaft of an engine.
A structure of an alternator for generating electric power required for an automobile using the automobile propulsion engine as a drive source is described for example in Japanese Patent Publication No. Tokukai Hei7-139550. FIG. 5 shows the alternator described in this Application. A rotation shaft 3 is rotatably supported inside a housing 2 by a pair of rolling bearings 4. A rotor 5 and a commutator 6 are disposed on an intermediate part of the rotation shaft 3. In addition, a driven pulley 7 is fixed to a portion protruding toward the outside of the housing 2, at one end (the right end in FIG. 5) of the rotation shaft 3. In the condition where it is assembled into an engine, an endless belt is spanned around the driven pulley 7, and the rotation shaft 3 is freely rotated by the engine crank shaft.
For the above described driven pulley 7, one which is simply fixed to the rotation shaft 3 has heretofore been used. On the other hand, various kinds of alternator pulley unit with a built-in one-way clutch have been proposed and used in part, such as one in which when the running speed of the endless belt is constant or tends to increase, motive power is freely transmitted from the endless belt to the rotation shaft, while when the running speed of the endless belt tends to decrease, the driven pulley and the rotation shaft are freely rotatable relative to each other. An alternator pulley unit with a built-in one-way clutch having functions described above, is described for example in Japanese Patent Publication Nos. Tokukai Sho56-101353, Tokukai Hei7-317807, Tokukai Hei8-614431) Tokukai Hei10-285873, Japanese Patent Publication No. Tokuko Hei 7-72585, France Patent Publication No. FR2726059A1 and the like. Moreover, such an alternator pulley unit with a built-in one-way clutch has been actually used in part.
FIG. 6 shows an alternator pulley unit with a built-in one-way clutch described in Japanese Patent Publication No. Tokukai Hei10-285873. This alternator pulley unit with a built-in one-way clutch has a sleeve 8 that can be freely externally fitted and secured to a rotation shaft 3 (FIG. 5). A driven pulley 7a is then disposed concentric with the sleeve 8 around the sleeve 8. In addition, a pair of support bearings 9 and a one-way clutch 10 are provided between an outer peripheral face of the sleeve 8 and an inner peripheral face of the driven pulley 7a. Of these, the support bearings 9 enable free rotation of the sleeve 8 and the driven pulley 7a relative to each other, while rotatably supporting a radial load applied to the driven pulley 7a.
Moreover, the one-way clutch 10 can transmit a turning force from the driven pulley 7a to the sleeve 8 only when the driven pulley 7a has a tendency to rotate in a predetermined direction relative to the sleeve 8. Therefore, to construct the aforementioned one-way clutch 10, a cam, face 12 is formed on an outer peripheral face of an intermediate portion of an inner ring 11 which is externally fitted and secured to the sleeve 8. Furthermore, a plurality of rollers 13 are arranged between the outer peripheral face of the cam face 12 and the inner peripheral face of the driven pulley 7a. Then, between these rollers 13 and a retainer 14 for retaining these rollers 13, there are provided a plurality of springs (not shown). These springs resiliently press the respective rollers 13 in a direction to make the respective rollers 13 encroach into a wedge shape at a portion where, of the dimensions of a cylindrical gap formed between the outer peripheral face of the cam face 12 and the inner peripheral face of the driven pulley 7a, the width across the diametral direction becomes narrow. Furthermore, a torque for pressing the respective rollers 13 based on the resilience is designated as 4 Nxe2x80xa2m or less.
According to the alternator pulley unit with a built-in one-way clutch described in the above described Japanese Patent Publication No. Tokukai Hei10-285873 constituted as described above, generating efficiency of the alternator can be ensured to some degree. That is to say, when the rotational speed of the engine increases, and the running speed of the endless belt 15 spanning between the drive pulley and the driven pulley 7a tends to increase, there is a tendency for the driven pulley 7a to rotate relative to the sleeve 8 in a predetermined direction. As a result, the respective rollers 13 encroach into the wedge shape (become locked) at the portion where, of dimensions of the cylindrical gap formed between the outer peripheral face of the inner ring 11 and the inner peripheral face of the driven pulley 7a, the width across the diametral direction becomes narrow, thereby enabling free transmission of the turning force from the driven pulley 7a to the rotation shaft 3. On the other hand, when the rotational speed of the engine decreases, and the running speed of the endless belt 15 tends to decrease, the driven pulley 7a rotates relative to the sleeve 8 in the direction opposite to the above described predetermined direction. Therefore, the respective rollers 13 shift to a portion where the width of the above described cylindrical gap becomes wider, enabling free rolling of these respective rollers 13 in the concerned portion (giving an overrun state), so that the driven pulley 7a and the rotation shaft 3 can freely rotate relative to each other. At this time, since the respective rollers 13 are pressed by means of a torque of 4 Nxe2x80xa2m or less based oil the resilience of the aforesaid respective springs, shift from the locked state to the overrun state can be performed at a relatively early stage from when the running speed of the endless belt 15 starts to decrease. Since the shift to the overrun state is performed at a relatively early stage as described above, the rotation shaft 3 of the alternator can continue to rotate in a high region to some extent based on its own rotational force of inertia, regardless of variations in the rotational speed of the engine, so that the power generating efficiency of the alternator can be ensured to some degree.
In the case of the alternator pulley unit with a built-in one-way clutch described in Japanese Patent Publication No. Tokukai Hei10-285873 constituted and operated as described above, it still cannot be said that the power generating efficiency is sufficiently ensured. In addition, there is the possibility of the occurrence of abnormal sounds due to rubbing of the driven pulley 7a and the endless belt 15 against each other, and a decrease in the life span of the endless belt 15 cannot be sufficiently prevented. That is to say, since the crank shaft is rotated and driven based on intermittent explosions inside the engine cylinder, completely smooth rotational motion is not performed, and the turning angular velocity varies slightly even during one rotation. The variation in the turning angular velocity increases as the rotational speed of the engine decreases. As a result, the running speed of the endless belt 15 spanning to the drive pulley secured at the end of the crank shaft also varies slightly. Therefore, to ensure sufficient power generating efficiency of the alternator, it is necessary to make the pulley unit follow the slight variations in the running speed of the endless belt 15, and to promptly perform the shift from the locked state to the overrun state when the running speed of the endless belt 15 tends to decrease.
On the other hand, even if the running speed of the endless belt 15 varies slightly as described above, the rotation shaft 3 of the alternator rotated and driven via the driven pulley 7a by the endless belt 15 does not vary so abruptly, based on the rotational force of inertia of the rotation shaft 3, and the rotor 5 and the commutator 6 secured to the rotation shaft 3. Hence, there is a tendency for the inner peripheral face of the endless belt 15 and the outer peripheral face of the driven pulley 7a to rub against each other in opposite directions. As a result, a stress in different directions acts repeatedly on the endless belt 15 which is rubbed against the driven pulley 7a, so that slipping occurs between the endless belt 15 and the driven pulley 7a. Hence, abnormal sounds are likely to occur due to this slipping, or the life span of the endless belt 15 is shortened.
The decrease in the life span of the endless belt 15 based on the friction between the outer peripheral face of the driven pulley 7a and the inner peripheral face of the endless belt 15 as described above actually arises also due to repeated acceleration and deceleration at the time of traveling. That is to say, at the time of acceleration, a drive force is transmitted from the endless belt 15 to the driven pulley 7a, while on the contrary, at the time of deceleration, a braking force acts from the endless belt 15 on the driven pulley 7a that tends to continue rotation based on the inertia described above. The braking force and the above described drive force act on the inner peripheral face of the endless belt 15 as a frictional force in opposite directions, resulting in a decrease in the life span of the endless belt 15. In particular, in the case of a vehicle provided with an exhaust brake such as a truck, the deceleration at the time of decreasing rotation of the crank shaft in the accelerator-off state is considerable. Based on the above described braking force, a frictional force applied on the inner peripheral face of the endless belt 15 increases, and as a result, the life span decreases noticeably.
To solve the various problems described above, it has been heretofore proposed to use a pulley with a built-in one-way clutch as the pulley for an alternator. In the case of the structure described in the aforementioned Japanese Patent Publication No. Tokukai Hei10-285873 however, the torque for pressing the respective rollers 13 constituting the one-way clutch 10 in a predetermined direction is as large as 4 Nxe2x80xa2m. Therefore, the structure described in Japanese Patent Publication No. Tokukai Hei10-285873 can cope with a relatively large variation in the rotational speed of the engine, but it is unlikely to cope with slight variations in the turning angular velocity occurring during one rotation of the crank shaft. If the pulley unit cannot cope with slight variations in the turning angular velocity of the crank shaft, then not only can the rotation of the rotation shaft 3 of the alternator not be maintained in a high rotation region, but also stress in opposite directions acts repeatedly on the endless belt 15 which is rubbed against the driven pulley 7a as described above. As a result, there is a possibility that the power generating efficiency of the alternator cannot be sufficiently ensured, or that the occurrence of abnormal sounds due to slipping between the endless belt 15 and the driven pulley 7a, and a decrease in the life span of the endless belt 15 cannot be sufficiently prevented.
Moreover, in the case of the alternator pulley unit with a built-in one-way clutch described in Japanese Patent Publication No. Tokukai Hei10-285873, only the size of a torque for pressing the respective rollers 13 constituting the one-way clutch 10 in a predetermined direction is addressed to ensure the power generating efficiency, and this torque value is designated as 4 Nxe2x80xa2m or less. However, when the running speed of the endless belt 15 tends to decrease, and it is necessary to rotate the driven pulley 7a relative to the rotation shaft 3 of the alternator in the direction to give overrun, not only does the torque for pressing the respective rollers 13 in the predetermined direction become an actual resistance to the rotation, but also the rolling rotation resistance of the respective support bearings 9 disposed on opposite sides of the one-way clutch 10, and the sliding resistance of seal members disposed between the driven pulley 7a and the sleeve 8 which are attached to end portions of the respective support bearings 9 becomes an actual resistance to the rotation. Therefore, in the case of the conventional structure described in Japanese Patent Publication No. Tokukai Hei10-285873, the torque necessary to rotate the driven pulley 7a relative to the rotation shaft 3 of the alternator in the direction to give overrun, actually increases to larger than 4 Nxe2x80xa2m. When in this way the torque increases, the torque which becomes a resistance against rotation in the direction to give overrun, suppresses the rotation based on the rotational force of inertia of the rotation shaft 3 or the like. Therefore it becomes more difficult to sufficiently ensure the power generating efficiency of the alternator, or to sufficiently prevent the occurrence of abnormal sounds due to slipping between the endless belt 15 and the driven pulley 7a, and a decrease in the life span of the endless belt 15.
In view of the above situation, the present invention has been developed for ensuring the power generating efficiency of the alternator and preventing the occurrence of abnormal sounds and a decrease in the life span of the endless belt.